High resolution aircraft radar antenna

ABSTRACT

A high resolution aircraft radar antenna having a pair of long alternately activated radio frequency (RF) antenna arrays in back-to-back relation within an elliptical cross-sectional boom of good aerodynamic characteristics supported on a retractable mounting from an aircraft and capable of producing slow boom rotation beneath the aircraft in the extended condition and streamlined with the fuselage in the retracted position for low drag to provide 360* radar search scanning and tracking operation.

0 United States Patent 1 1 1111 3,766,561

Johnson Oct. 16, 1973 HIGH RESOLUTION AIRCRAFT RADAR 3,058,107 10/1962 Danielson 343/876 x ANTENNA 2,702,346 2/1955 Evans et al. 343/872 X 3,026,516 3/1962 Davis 343/705 [75] Inventor: Francis B. Johnson, Northridge,

Cahf' Primary Examiner--Carl D. Quarforth [73] Assignee: The United States of America as Assistant Examiner-Joseph P Otenza represented by the Secretary of the Attorney-R. Sciascia and Collignon Navy, Washington, DC. 22 Filed: Dec. 30, 1969 [57] ABSTRACT A high resolution aircraft radar antenna having a pair [21] Appl 4793 of long alternately activated radio frequency (RF) antenna arrays in back-to-back relation within an ellipti- [52] US. Cl 343/705, 343/876, 343/763 Cal t onal boom of good aerodynamic charac- [51] Int. Cl H01 128 t ri upp t d n a retractable mounting from an [58] Field of Search 343/705, 872, 713, aircraft and capable of producing Slow boom rotation 343/876, 100 SA beneath the aircraft in the extended condition and streamlined with the fuselage in the retracted position [56] Referen e Cited for low drag to provide 360 radar search scanning UNITED STATES PATENTS and tracking Operatwm 2,984,834 5/1961 Howard et al. 343/705 2 Claims, 4 Drawing Figures ALTERNATE SWITCHING CIRCUIT PATENTEDucnems 3.766561 ALTERNATE SWITCH CIRCUI SINGLE ARRAY l l I l I l l l l 1 VELOCITY KNOTS INVENTOR.

FRANCIS B. JOHNSON FIG 4 I A TTORNE Y5 :1 I-I IGIIERESOLUTION AIRCRAFT RA'DAR ANTENNA BACKGROUND OF THE INVENTION This 'inventionrelates to aircraft search radar antenna arrays and more particularly to rotatable type antenna arrays which .are extendible below an aircraft body'for scanning throughout'360'degrees.

Known antennas of this typeiutilizea single antenna array that is rotated at some desired speed, usually about six revolutions perminuteThere are severelimitations on the-scanning speed used:inaircraftenvironments such'that the speed of6-RPM for a single'antenna array cannotsbe increasedtospeed up search operations, particularly with the addition to the array length to increase the:aperture', as wouldappear to :be the :most economical solution. Such a slowscanning rate'makes the aircraft carrying the antenna vulernable toundetected .fast moving enemy aircraft, particularly when both aircraft 1 are closing.

SUMMARY OF THE INVENTION .of only 3 RPM thescan-will be equivalent to that of the single array antenna rotating at 6-'RPM with equalapertures but the apertures can be increasedin the dual .arraybyadditional array length to improve resolution.

The two antenna arrays are alternately pulsed which provide increased accuracy by halving the rate of rotation per antenna array and increasing theaperture of each antennas'lt is accordingly a-general object of this invention to providean extendibleand rotatable search antenna for aircraft'havin'g apair of back-to-back antenna arrays of wide aperturein a streamlined enclosure'for slow rotational omni search scan.

BRIEF DESCRIPTION OF THE DRAWING These and other objectsand the attendant advantages," features,- and uses-willbecome more apparent as the 'descriptionproceeds when takeniin consideration withthe accompanying drawing in which:

. FIG. 1 illustrates a head-onelevational view of a twin engine aircraftshowing the antennaarray of this invention in its extended positionand the retractedposition in dotted lines;

FIG. 2 illustrates .a sideelevation ofthe aircraft'and antenna of-FIG. '1;

FIG. 3 illustrates a cross-sectional view of the antenna array taken on the line 33 in-FIG. l with an electric circuit thereto shown in block diagram; and

FIG. -4 provides a signal-to-noise plus clutter ratio graph comparing the antenna array of this invention with a singleantenna array.

'BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT Referring 'more particularly to FIGS. l 'and 2, FIG. 1

illustrates a twin engine aircraft l0=in a'head-on view while FIG."2'illustratesthis'aircraft in a side elevational view.Shown in 'theextended position'is the antenna array .11 supported from the aircraft fuselagebelly by any suitable retractable-extendible mechanism 12 of the type morefully described-in the US. Pat. No. to

Howard, .Ir. et'al. 2,984,834 and I-I.-'al., Evans et al.,

2,702,346. Since the extendible-retractable mechanism formsno part of this invention, and any suitable mechanism may'be used in this invention,'nofurtherdescription will be given'of this-mechanism. The antenna array l l in its extended position, as shown in FIGS. 1 and 2,

is operable to be rotated'for 360 degrees'antenna scanning, as willlater become more fully understood in the description of operation. The antenna 11 in its retracted position will be nestled in or against the fuselageibelly, as shown in dotted lines in FIGS. 1 and 2, to provide the least amount of drag in flight and clearance for take-o'ffsand landings when the antenna is not in use.

Referring more particularly to FIG. 3, the dual antenna array is shown in cross-section in which a main supporting beam 14 has rib members l5affixed thereto on opposite sides as to the right and to the left as viewed -in FIG. '3 in the same manner as ribs of an airfoil, wing, or the like, to support a shell member 16 of elliptical or oblong cross-sectional configuration. The

two small radii of curvature 17 of the shell consists of dielectric material which constitutes the microwave windows for the antenna arrays. Two or a pair of antenna arraysare mounted back-to-back on the beam 14 consisting of the waveguide assemblies 18 and the'horn structures 19. The waveguide assemblies 18 and horn structures are positioned between the rib members 15, as well understood by those skilled in the art, to provide proper transmission and reception of RF frequencies.

Between the ribs 15 and the dielectric covers 17 are waveguide lenses 20 to provide the proper lens systems for thedual array antenna waveguides in the transmission and reception of RF signal. RF signals are conducted'through each of the horns 19 betweenribs 15 and through the lens systems-'20 and through the dielectric covers 17 for transmission to illuminate targets and for reflection of any targets within the beam width of the antenna. These transmitted and received signals are by way of the conductor means 21 through an alternate switching circuit 22 to and from the transmitter and receiver circuit '23, as shown in block circuit schematic in FIG. 3. The alternate switching circuit 22 is of any well known type such as ferrite or varactor type microwave switches described in the texts of Radar Handbook by Merrill. Skolnik, 1970, published by McGraw- I-IillBook Company,pages 8-25, 26 and Airborne Radar, Principles of Guided Missile Design, 1961, published byD. Van Nostrand Co., Inc., pages 56l2. The alternate switching circuit 22 energizes the right and left antenna arrays, as shown in FIG. 3, alternately so that for'every revolution of the antenna array 11 both antennas willagive complete 360 scanning over the RPM is ordinarily used with an antenna for an aperture or length of approximately 30-feet. Any increase in this aperture or length of the antenna array causes complications inany attempt to increase the rotational speed of the antenna and, accordingly, this 30 feet of antenna array and the rotational speed of the antenna is limited. In the present invention the aperture can be increased to 50 feet or more in antenna array length which greatly improves the resolution of the antenna. This is possible by virtue of the back-to-back antenna array which allows a decrease in rotational speed to about 3 RPM providing the same antenna coverage with higher resolution.

OPERATION In the operation of the dual antenna array the antenna is first extended by the mechanism 12 in the aircraft and rotated at 3 RPM with the transmitter and receiver in the operative condition to alternately pulse the dual antennas. This will provide a single-to-noise plus clutter ratio in comparison with a single array, as shown in FIG. 4. Let a the aperture, the RPM, and A the period of the single and dual antennas. For a single antenna w 6 RPM A 10 See.

For the dual antenna of this invention (.0 3 RPM A 10 Sec.

With the above operative conditions it may be realized from the illustration in the graph of FIG. 4 that the dual antenna array of this invention provides a higher signalto-noise plus clutter ratio S/(N C) than that of a single antenna array. As shown in FIG. 4 both single and dual arrays drop off in the signal-tonoise plus clutter ratio as the velocity in knots increases.

While only a preferred embodiment is shown to describe the invention, applicant desired to set out the spirit of his invention by the scope of the appended claims.

I claim:

1. A high resolution aircraft radar antenna that is extendible for rotation and retractable for low drag storage on an aircraft comprising:

a pair of elongated antenna arrays supported together in back-to-back relation on a beam;

an elongated elliptical shell housing said pair of antennas and supported on said beam with the two edges of short radii being of dielectric material to provide opposite microwave windows for said pair of antenna arrays therein, said shell having a central support on one long radius of curvature attachable to an aircraft for controlled retraction, extension and rotation thereof; and

a switching circuit coupled between said pair of antenna arrays and a radar transmitter and receiver to alternately activate said pair of antenna arrays whereby support of said central support on an aircraft for retraction, extension and rotation of said pair of a ntenna a rrays activated alternately prov vides two scans i81 apart per revolution of said antenna arrays.

2. A high resolution aircraft radar antenna as set forth in claim 1 wherein said support of said shell on said beam includes ribs placed radially along the longitudinal length of said shell interior between array waveguide openings and fixed to said beam with microwave lenses supported in said shell between said ribs and said dielectric material providing microwave transmission therethrough. 

1. A high resolution aircraft radar antenna that is extendible for rotation and retractable for low drag storage on an aircraft comprising: a pair of elongated antenna arrays supported together in backto-back relation on a beam; an elongated elliptical shell housing said pair of antennas and supported on said beam with the two edges of short radii being of dielectric material to provide opposite microwave windows for said pair of antenna arrays therein, said shell having a central support on one long radius of curvature attachable to an aircraft for controlled retraction, extension and rotation thereof; and a switching circuit coupled between said pair of antenna arrays and a radar transmitter and receiver to alternately activate said pair of antenna arrays whereby support of said central support on an aircraft for retraction, extension and rotation of said pair of antenna arrays activated alternately provides two scans 180* apart per revolution of said antenna arrays.
 2. A high resolution aircraft radar antenna as set forth in claim 1 wherein said support of said shell on said beam includes ribs placed radially along the longitudinal length of said shell interior between array waveguide openings and fixed to said beam with microwave lenses supported in said shell between said ribs and said dielectric material providing microwave transmission therethrough. 